1. Field of the Invention
The present invention relates to an air-conditioning device for a hybrid vehicle which is driven by an internal combustion engine and an electric motor.
2. Description of Related Art
A hybrid vehicle is usually powered by an electric motor when it is starting and being driven at a low speed, by an internal combustion engine when it is driven at a normal speed, and by both of the motor and the engine when it is being accelerated. Air conditioning devices for such hybrid vehicles are disclosed, for example, in JP-A-6-286459 and JP-A-5-328521. In those conventional air conditioning devices, the engine is automatically started to drive a compressor for an air conditioner when air-conditioning is required, even when the vehicle is powered by the electric motor. Electric power for driving the compressor is saved in this manner. In those devices, however, the engine is compulsorily operated to drive the compressor when the engine power is not necessary to drive the vehicle. Moreover, the engine is operated to drive the compressor even when the vehicle comes to a halt at an intersection, for example. Therefore, fuel is consumed unnecessarily and fuel economy is sacrificed.
To improve the fuel economy, it is conceivable to stop the engine compulsorily when the vehicle comes to a halt at an intersection even if the air conditioning switch is being turned on. If the engine is stopped and the compressor is not driven, the air-conditioner does not function and comfortability of passengers is sacrificed. In addition, condensed water on a surface of an evaporator is evaporated again during a halt of the vehicle, thereby causing frost on a windshield. The more frost will cover the windshield, the longer the vehicle halts.